Electromechanical oscillator



1943- M. MORRISON 2,456,442

ELECTROMECHANICAL OSCILLATOR- Filed Nov. 6, 1945' 2 Sheets-Sheet 2 Elma/whom Patented Dec. 14, 1948 UNITED STATES PATENT OFFICE ELECTROMECHANICAL OSCILLATOR Montford Morrison, Upper Montclair, N. J. Application November 6, 1945, Serial No. 627,055

This invention relates to electromechanical oscillators employing a grid-controlled electron dischargetube having motional impedance in the plate circuit thereof.

This is in part a continuation of patent application Serial No. 496,389, filed July 28, 1943, now issued'as Patent No. 2,415,022.

Among the objects of the invention are: to provide an electromechanical oscillator, driven by a grid-controlled electron discharge tube having motional impedance in the plate circuit thereof, with an operating frequency which is substantially independent of the motional impedance; to provide an electromechanical oscillator, driven by a grid-controlled electron discharge tube having a motional impedance in the plate circuit thereof, which impedance is non-oscillatory in character, allowing the oscillator to operate over a wide range of frequencies, and to provide an electromechanical oscillator, driven by a grid-controlled electron discharge tube having motional impedance in the plate circuit thereof, in which the frequency of the motional impedance is caused to follow the natural period of an independently oscillating system.

This invention may be employed in many instrument and apparatus applications for the generation of precise audio frequencies, precise timing in optical systems, in the construction of measuring and testing devices, for the synchronous operation of signal devices as well as for further and other applications, which will be obvious upon reading the specification and claims hereof. By the employment of this invention, small, compact and light motor mechanisms may be constructed with speed regulations better than 0.01% and the present invention is applicable to devices and apparatus requiring this constancy of speed.

The invention will be more fully understood from the following description when read in connection with the accompanying drawings, Fig. 1 of which is a circuit diagram of an arrangement embodying the principles of the invention in simple form for clearness in explaining the basic operating characteristics of the invention;

Fig. 2 is a side view illustrating in some detail the type of motor mechanism employed in the embodiment described herein;

Fig. 3 shows curves of electrical circuit char acteristics, useful in understanding the present invention; I v

Fig. 4 is a fragmentary drawing of part of th rotor illustrative of the term rotor phase angle in connection herewith as used herein.

8 Claims. (01. 256-36) Referring to Fig. 1, which is an alternatingcurrent motor which may, in practice, be any one of the many types which can be made to operate synchronously with an applied alternating voltage. This motor may be of the inductor type with salient poles, a direct current field type with winding rotor having no salient poles, it may be of the phonic wheel type, or any other suitable substitution.

In the embodiment shown in Fig. l, I employ an inductor type motor with permanent magnet fields and of a type commonly used as a synchronous motor or an alternating-current generator.

The field member 2, Figs. 1 and 2, is of a laminated structure having a permanent magnet member 3, Figs. 1 and 2, which supplies the constant magnetic field for the motor. The teeth of the stator are so spaced angularly with reference to the rotor that the main magnetic circuit created by the permanent magnet 3 flows first through coil 5 and then through coil 4, and as the rotor' 6 revolves, alternating current is produced between terminals 1 and 8.

The operation as described above is really that of a generator, but of course when alternating current is fed through windings 4 and 5 under proper conditions, the device may act as a motor. This is a simple illustration of a common type of motor and generator found in the communication industry and will be understood by those familiar with the art to which the present invention appertains.

However, in common practice, this device, when used as a motor, is supplied with alternating current fromsome source of alternating current.

supply, such as the tuning fork generator with an amplifier to bring a power level up to a value suflicient to operate the motor.

Under these conditions a high constancy of speed control can be obtained but only at a very high apparatus cost and with an excessive amount of weight. Such a motor so operated also has, like all synchronous motors, a distinct tendency to hunt, "and while the mean frequency of such a combination may have a very high precision of constancy, the instantaneous frequency value may and often does very badly, thus making such a device unsuitable for certain types of precision work where agcomplete absence of hunting is essential.

In the employment of my invention there is a complete absence of hunting, which will be hereinafter'm'ore fully described.

The winding of electric motor I is connected push-pull to the output of twin triodes 9 supplied with plate current by battery Ill. The grids of the twin triodes 9 are connected across a capacitance-inductance parallel oscillatory system I I, the center 12 of which is connected with cathodes of the twin triodes 9.

The oscillatory system I I is connected through feed-back circuits l3 and 14 to the plates of the twin triodes 9 which are, as before stated, connected push-pull tothe windings 4 and 5.

These feed-back circuits l3 and I4 are constructed along the lines of feed-back circuits used in resistance stabilized audio frequency oscillaa tors. That is, the condensers employed are large in capacity for the frequency employed and the resistors are very high in comparison with the plate resistance of the twin triodes. The impedance of these feed-back circuits is such that the voltage developed across the oscillatory system H does not sensibly affect the value of the feed-back current. The resistors of the feed-back circuits are also sufficiently high so that the current through these feed-back circuits is substantially of the form and phase of the voltage across the windings 4 and 5 of the motor I.

With such characteristics these feed-back circuits may be referred to as having a resistance current-limiting characteristic. In other words, the form and phase of the current through these resistors is such as is produced by a pure resistance, the impedance of the condensers and the oscillatory circuit being so small in comparison that they contribute no sensible effect upon the circuit impedance. Two feed-in circuits l5 and It are also provided so that when switches I1 and I8 are closed, alternating current from source I9 may be fed into the oscillatory system I I with or without feed-back current. The feed-in circuits l5 and I6 are, as illustrated, similar to circuits I3 and I4; that is, the impedances are high in comparison with the plate resistance of the tube.

Referring to Fig. 1, I may provide an electrical load at the position so designated and I- may introduce a condenser 20' by closing the switch 2|. By so doing I provide tuning forthe motor winding which is useful in some applications.

Referring to Fig. 2, there is illustrated on the shaft 22 a metal disc 23 which may be caused to revolve in the field of a permanent magnet 24 producing an eddy current brake as a load on the device which is referred to hereinafter as mechanical load.

Since the feed-back circuits l3 and [4 have purely a resistance characteristic, the current follows the form, amplitude and phase of the voltage across terminals 1 and 8, but the voltage developed across parallel oscillatory system II will rise and fall according to the resonance curve of the oscillatory system, as a function of the frequency, as is well understood by those skilled in the art.

In Fig. 3 is the general form of the voltage curve as a function of the frequency with the resonance value indicated, as is commonly illustrated. Also, the phase angle of this voltage curve is illustrated in Fig. 3. Since the current lags the voltage for resonance frequency in such a system, the voltage then leads the current over similar range of frequencies. The phase angle curve is slightly displaced depending upon the Q of the circuit.

It will be appreciated from Fig. 3 that oscillatory system H produces a grid-contro1 which not only gives amplitude variations as a function of 4 and 5 is indicated by the letter 0.

the voltage but phase angle variations as a function of the voltage.

The current through windings 4 and 5 has a phase displacement with the voltage at terminals 1 and 8. This phase displacement makes is possible to us the voltage feed-back from terminals 1 and 8 through feed-back resistors l3 and I4 to provide the proper phase angle for the current which is produced by grid control through the twin triodes 91 The phase angle of the plate current of the twin triodes 9 is, of course, affected by the electrical load, so designated, tuning 20 so illustrated, or by mechanical loading, as described in Fig. 2.

However, the phase angle between the voltage and the current in the windings 4 and 5 are not affected by these added parameters.

The speed at which the rotor B operates depends upon the phase angle, between the voltage and current in the windings 4 and 5 and the mechanical loading on the rotor, different speeds having. difierentphase angles.

Referring to Fig. 4', the angular phase position between the rotor and the current in windings The more the mechanical loading the larger the angle 0, this lagging position accounting for the increased torque demand caused by the increased loading, as is' well understood by those familiar with the art of'synchronous motor operation.

In some respects this motor operates like a synchronous motor, but its speed is determined by its own characteristice rather than that of an external generator.

Its speed characteristics, being determined mainly by the phase angle, between the voltage and the current in its windings and the mechanical loading, means that-the motor will run at a speed and only at that speed, corresponding to the phase angle of the current supplied to the motor, with reference to the voltage across its windings.

Of course, such a motor has to be brought up above itsoperating speed and allowed to coast back into the operating speed, but the speed at which it continues to operate always depends mainly upon these two factors above started.

If the motor is brought up to a certain high speed and allowed to coast it falls to a frequency at which the oscillatory system H will provide the right phase angle for the requirements.

The voltage has very little effect upon the speed of the motor, even sometimes over a range of increase in voltage. As a matter of fact, within operating ranges the voltage is so unrelated to the speed of the motor that it is possible to make adjustments so that the motor slows up with increased voltage and speeds up with a decrease in voltage.

In the ordinary synchronous motor, the motor is attempting to operate through a somewhat elastic system with a fixed sources of frequency and the elasticity of this system together with the inertia of the partsconstitute a more or less electromechanical oscillatory system in the rotor itself, commonly known as hunting.

This motor hasno tendency whatever to hunt as there is no elastic connection between the rotor of the motor and its source of supply, this relation is fixed and rigid and one follows the other perfectly and therefore there can be no hunting.

In a well designed motor having a good strong direct-current field the embodiment of my invention produces a comparatively high torque motor with a high apparatus efficiency and high electrical eflicie'ncy' and-is'entirely unlike small synchronous motors with their comparatively high current inputs and low torques, to say nothing of the instability due to hunting.

A complete analysis of this invention in all of its'analytical aspects, is beyond the scope of a patent application, but the applicant giveshereunder a description of the operation of the device which points out all operating characteristics essential to an understanding of the invention by those skilled in the art to which it appertains.

An over-all understanding of the operation of the device, both as a motor and as a generator, may behad from a consideration of its opera tion as one machine of a motor-generator set,

. in which the motor or generator device illustrated in Figs. 1 and 2 is considered as coupled through shaft 22 to the shaft of a direct-current motor, the-said. direct-current motor having speed adjustmentby armature voltage control. The eddy current disk 23 may be considered as removed for simplicity of description.

Switches l1, l8 and 2| will be considered as open and the above-described two-machine set will be started up by supplying voltage to the above-described shunt motor, as the device as illustrated in Figs. 1 and 2 is not supplied with a self-starting feature.

The assumed shunt wound driving motor must be taken as a size which is comparable with that of the motor device illustrated in Figs. 1 and 2',

so that in the description of the operation, the shunt motor may be called upon to drive. the motorin Figs 1 and 2, and the motor illustrated in Figs. 1 and 2 may be called upon to drive the assumed shunt motor. In this way, either machine of the two-machine set may act as a motor or as a generator, depending upon the constants of these two motors and the voltage level at the terminals of the shunt motor, when both machines are mechanically coupled and bothmachines are connected to their respective power sources.

This motor-generator reversibility-of-operation is commonly met in electrical power substation art in which, for instance, two operationally reversible dynamo electric machines are mechanically coupled together and individually coupled to different power lines. Such machines are sometimes so connected, one machine to a directcurrent power circuit and the other machine to an alternating-current power circuit, that transfer of energy may be made from either of the circuits to the other thereof, depending upon to which circuit it is desired to supply energy from the other thereof.

Under the conditions described,either machine will act as a motor and either machine will act as a generator, and the factor which determines which machine of such a set acts as a generator or as a motor, is whether the voltage supplied to the machine in question is higher than the voltage it generates from being operated by the other machine acting as a motor. Thus in the case cited, transfer of energy from the alternatingcurrent power line to the direct-current power line, or vice versa, may be accomplished by simply raising or lowering either one of the supply line voltages at the terminals of the machine to which it is connected. Commonly this is done by induction voltage regular adjustment on the alternating current machine.

Referring back to the device illustrated in'Figs. 1 and 2, considered as a part of the motor-generator set described; if the shunt motor is adjusted re'nt'motorof Figs. -1 and 3, up to a speed which corresponds to that indicated in Fig. 3 by the designation resonance frequency and then the operating circuits of Fig. 1 closed with the tuned circuit ll adjusted to the same said resonance frequency, this motor-generator set arrangement is said to float"-between the two sources of potential, one source supplying the alternatingcurrent motor and the other one supplying the direct-current motor. If perfect electrical balance between the voltagesof the two machines were possible, theoretically each machine would draw just enough power from its own 'circuitto maintain its speed, from'its own power source, that is, one machine would draw from its own power source, and likewise the other machine would draw from its power source, just enough energy to maintain each at the'said fixed speed. Referring to Fig. 3, it can now be pointed out how the machine of Figs. 1 and 2 may operate inthe same circuit either as a motor or as a generator. .1

Returning to the operating position described above in which each machine is theoretically operating as a motor; if the armature voltage of the shunt motor is dropped slightly, the shunt motor will act as a generator, for reasons pointed out above, and becomes a load forthe alternativecurrent motor. However, if the armature voltage of the shunt motor is raised, the speed of the set tends to increase above the so-called resonance frequency and the alternating-current motor acts as a generator in the exact same sense as doesthe motor-generator set in the power substation above referred to. I Thus, the one circuit illustrated in Fig 1 and the one set of curves illustrated in Fig. 3, serve to illustrate the operation of the device both as amotor and as a generator. 1 a It is obvious upon inspection of Fig.. 3, if the phase angle of the current below resonance frequency-issuch as to produce torque in the alter nating-current motor, when the phase angle of the current is reversed for speeds above resonance frequency, the machine cannot be taking energy from the circuit but must be delivering energy to this supply circuit. The phase angle curve shown in Fig. 3 is very similar to the speedtorque of alternating-current induction motors, which are likewise known to act'as generators when their rotors are driven in excess of synchronous speed, which corresponds with the res-.

onance frequency speed of Fig. 3.

In fact, a-motor-generator set such as de scribed, which includes the motor device of Figs. 1 and 2, results in a very practicalspeed control device for any suitable sort of a driving motor used inplace of the described shunt motor, where the size and speed-torque characteristics of the driving motor are properly selected. When the speed of such a motor-generator set tends to reduce, the motor device of Figs. 1 and 2 at once begins to act in the capacity of a motor and assists in maintaining the speed, and likewise, if the speed of the set tends to increase, the alternating-current motor of Figs. 1 and 2 begins to act as a generator and loads up the driving motor, thus stabilizing the speed thereof.

In the case of the operation of the device shown in Figs. 1 and 2, without consideration of any second machine, the device can be cons'idered ias started up by a starting motor to a speedin excess of'the resonance frequency speed referred to, and'thnby electricallyl disconnecting 7 the starting motor from its supply line, ,thealternating-current motor of Figs. 1 and 2 will continue to. operate if not overloaded, and in accordance with thesame characteristics: as illustrated in Fig. 3, as the operation of the device under these conditions is identicallyas described above.- with the. exception of the fact that the alternating-current motor alone has no abilityto exceed the resonance frequency speed and therefore operates always at or below thisfrequency and in accordance with. those arts of the curves in Fig. 3 lying in the frequency ranges below the said resonance frequency.

The high frequency-stability of themotor arises from a combination of several phenomena.

As the speed of the motor approaches that corresponding to resonance-frequency, the angle of lag. of the current rapidly approaches zero so that an increase in magnetic-field strength is directly accompanied by corresponding decrease in the'phase angle of the current, which results in neutralizing any tendency to increase in speed.

Referring toFig. 4, the phase of thecurrent producing the torque in the rotor has. to lag behind the voltage of the system by a phase angle which corresponds in some relation to the relative lag of the synchronous phase position of l the rotor in order to produce torque. This corresponds somewhat to. the so-called" v curve'of synchronous motor operation, that is, the flux through the air-gapbetween the stator and the rotor must reach its maximum value before synchronous registratton between the teeth thereof or. else no torque is developed between the rotor and the stator, which corresponds again somewhat to the so-called V-curves' of synchronous motor operation.

Since the circuit in Fig. 1 corresponds, in so far as feed-back is concerned, to an audio frequency resistance-stabilizer oscillator arrangement, the oscillatorycircuit H possesses ahigh degree. of frequency stability which may be in excess of .01 as is well known in the are relatingtoresistance-stabilized audio frequency oscillators.

With the switch 2| remaining open; the coils l and slot stator 2 function as ahigh impedance primary of a push-pull transformer and do not fimction to influence the frequency characteristics of the rotor speed. However, with switch 2] closed, an oscillatory characteristic developed thereby can be made to influence the motor speed.

In common practice, the closing of sWitch'Zi functions principally to change the impedance characteristics of the motor stator circuit; if and when desired.

As pointedout supra, thedesign-and adjustment'of the circuits may be such that the speed. ofrotor 6. can be made to increase with a decrease in the voltage of battery l0, and vice ver: sa, the speed of the rotor 6 may be caused to decrease with an increase in battery voltage. Likewise, additional loading of the rotor may or may not aifect the speed thereof, depends ing upon the circuit adjustments involved and the amount of loading.

Any changein speedof rotor 6 due to change in loading of the said'rotor, is a result of the reaction of the loading on the connected circuits rather than a characteristic of the principle ofoperation.

Since, in a practical device which may be of a. size represented by the original drawing taken asfull scale, the current in feed back resistors- Is and llisonlyof the'magnitude of acouple .hundredmicro-amperes; very little energy is required for the oscillatory circuit 1 I, and therefore, the addition or subtraction of very little energy from this circuit at or near the natural period thereof, serves to influence it markedly. Therefore, if and'when it is desired to synchronize theoperation of the motor device with an external alternating current source such as In, this may be very effectively done by closing switches l1 and is which serve to effectively lock in the local oscillating system [I with the independent external source of alternating current 19,. by synchronous injection of voltage, as is well understood in the electronic tube synchronizing art.

When a conventional type of synchronous motor is synchronized on an alternating-current line,.particu1arly when it is not operating at exactly the synchronous speed of the alternating current line, the rotor of the synchronous motor may oscillate considerably or hunt, as it is usually called, until this transient condition has subsided. However, in closing switches H and I8 with source-f9, the rotor speed of motor I is synchronously locked-in with source I9 and no oscillatory or hunting transient is manifested in this operation as stroboscopic tests show that the rotor 6 changes its speed from that determinedby theoscillatory system H to the determined by the frequency of source I!) directly withoutany hunting phenomenon whatsoever.

The applicant does not limit himself to the structure shown in the described embodiment.

- The limitations of the invention are set forth in theclaims hereunder.

What I claim is:

1. An audio-frequency oscillation generating system comprising an electronic discharge tube having a cathode and a plate with an electrostatically cooperating discharge-control electrode, a plate circuit having an aperiodic natural inotional impedance and including a source of discharge energy, a control-electrode tank circuit having a natural period of oscillation independent of said motional impedance, 3. feed-back circuit from said plate circuit to said tankcircuit including a feed-back circuit member having a high impedance compared to the plate resistance of said tube, an integral source of voltage having a predetermined periodic oscillation independent of said tank circuit, and a coupling circuit between said source and said tank circuit including a coupling circuit member having a high impedance compared to the plate circuit of said tube, whereby said motional impedance is caused to followthe periodic oscillations of said source.

2. An audio-frequency oscillation generating system comprising an electronic discharge tube having a cathode anda plate with an electro statically cooperating discharge-control electrode, a plate circuit having an aperiodic natural motional impedance and including asource of discharge energy, a control-electrode tank circuit having a natural period of oscillation independent ofsaid motional impedance,- a feed-back circuit from said plate circuit to said tank circuit including a feed-back circuit member having a high impedance compared to the plate resistance of said tube, an integral source of voltage having a predetermined periodic oscillation independent of said tank circuit, and a coupling circuit between said source and said tank circuit including a coupling circuit member having a high impedance compared to the plate circuit of said tube, where by said motional impedance is caused to follow the periodic oscillations of said source and appreciably independently of the natural period of said tank circuit.

3. An audio-frequency oscillation generating system comprising an electronic discharge tube having a cathode and a plate with an electro statically cooperating discharge-control electrode, a plate circuit having an aperiodic natural motional impedance and including a source of discharge energy, a control-electrode tank circuit having a natural period of oscillation independent of said motional impedance, an integral source of voltage having a predetermined periodic oscillation. independent of said tank circuit, said tank circuit having a two feed-in circuits, one of said circuits being coupled to said plate circuit, the other of said circuits being coupled to said integral source, and each of said circuits including a circuit member having a high impedance compared to the resistance of said tube, whereby said motional impedance is caused to follow the periodic oscillations of said source.

4. An audio-frequency oscillation generating system comprising an electronic discharge tube having a cathode and a plate with an electrostatically cooperating discharge-control electrode, a plate circuit having an aperiodic natural motional impedance and including a source of discharge energy, a control-electrode tank circuit having a natural period of oscillation independent of said motional impedance, an integral source of voltage having a predetermined periodic oscillation independent of said tank circuit, said tank circuit having two feed-in circuits, one of said circuits being coupled to said plate circuit, the other of said circuits being coupled to said integral source, and each of said circuits includin a circuit member having a high impedance compared to the resistance of said tube, whereby said motional impedance is caused to follow the periodic oscillations of said source and appreciably independently of the natural period of said tank circuit.

5. In an electronic tube audio-frequency oscillation generating system comprising an aperiodic natural motional impedance having a natural period of oscillation independent of said motional impedances and an integral source of voltage having a predetermined periodic oscillation independent of said natural period, a coupling circuit between said source and said tank circuit having a high impedance compared to the plate resistance of said tube, and a feed-back circuit from said plate circuit to said tank circuit having a high impedance compared to the plate circuit resistance of said tube, and last two said impedances being fixed to cause said plate circuit mo-' tional impedance to follow the periodic oscillations of said integral source of voltage.

6. In an electronic tube audio-frequency oscillation generating system comprising an aperiodic natural motional impedance having a natural period of oscillation independent of said motional impedances and an integral source of voltage having a predetermined periodic oscillation independent of said natural period, a coupling circuit between said source and said tank circuit having a high impedance compared to the plate resistance of said tube, and a feed-back circuit from said plate circuit to said tank circuit having a high impedance compared to the plate circuit resistance of said tube, and last two said impedances being fixed to cause said plate circuit motional impedance to follow the periodic oscillations of said integral source of voltage and appreciably independently of the natural period of said tank circuit.

'7. In an electronic tube audio-frequency oscillation generating system comprising a plate circuit, a control-electrode tank circuit having a natural period of oscillation independent of said motional impedance and an integral source of voltage having a predetermined periodic oscillation independent of said natural period, a high impedance coupling circuit feeding said voltage into said tank circuit, said voltage being amplified in said plate circuit, a high impedance circuit from said plate circuit feeding a part of said amplified voltage back to said tank circuit, and said high impedances being fixed to cause said motional impedance to follow the periodic oscillation of said source of voltage.

8. In an electronic tube audio-frequency oscillation generating system comprising a plate circuit, a control-electrode tank circuit having a natural period of oscillation independent of said motional impedance and an integral source of voltage having a predetermined periodic oscillation independent of said natural period, a high impedance coupling circuit feeding said voltage into said tank circuit, said voltage being amplifled in said plate circuit, a high impedance circuit from said plate circuit feeding a part of said amplified voltage back to said tank circuit, and said high impedances being fixed to cause said motional impedance to follow the periodic oscillation of said source of voltage and appreciably independently of the natural period of said tank circuit.

MONTFORD MORRISON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,599,922 Rathbone Sept. 14, 1926 1,660,084 Morton Feb. 21, 1928 1,941,445 Deisch Dec. 26, 1933 2,324,525 Mittlemann July 20, 1943 2,373,560 Hanert Apr. 10, 1945 2,415,022 Morrison Jan. 28, 1947 2,427,920 Morrison Sept. 23, 1947 

